It's because they're obsessed with the concept of race. People are intimately convinced that black people are all related (there is more genetic diversity in black Africa than in the rest of the world combined) and that white people are all related (whereas presumably successive waves of black Africans whitened independently as a genetic adaptation to less sunlight : white Neanderthals, white Cro-Magnons etc)

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}